Growth, nitrogen doping and characterization of isolated single-wall carbon nanotubes using liquid precursors Gayatri Keskar a , Rahul Rao b , Jian Luo a , Joan Hudson c , Jia Chen d , Apparao M. Rao b, * a School of Materials Science and Engineering, Clemson University, Clemson, SC 29634, USA b Department of Physics and Astronomy, Clemson University, 107 Kinard Laboratory of Physics, Clemson, SC 29634, USA c Advanced Materials Research Laboratories, Clemson University, Clemson, SC 29634, USA d IBM Research Division, T.J. Watson Research Center, Yorktown Heights, NY 10598, USA Received 25 May 2005; in final form 29 June 2005 Available online 21 July 2005 Abstract Isolated single wall carbon nanotubes (SWNTs) were prepared on bare quartz and SiO 2 /Si substrates using a chemical vapor deposition process in which xylene was used as the carbon source. Controlled doping of isolated SWNTs with nitrogen was achieved by mixing appropriate amounts of acetonitrile with xylene. As the nitrogen concentration in the feed was increased from 0 to 33 at.%, the radial breathing mode intensity decreased dramatically while the intensity of the D-band increased gradually relative to that of the G-band. The D 0 -band at 1620 cm 1 was observed in the Raman spectrum when the nitrogen concentration reached 2–3 at.%. Ó 2005 Elsevier B.V. All rights reserved. 1. Introduction Single-walled carbon nanotubes (SWNTs) have been used as the Ôbuilding blocksÕ in the fabrication of room temperature field effect transistors [1–4], diodes [5] and inverters [6]. For developing nanotube-based comple- mentary logic circuits, we need both p- as well as n-type carbon nanotube field effect transistors (CNTFETs). Current devices based on as-grown isolated SWNTs are invariably p-type in behavior and degassing them leads to n-type characteristics [7]. However, the p-type characteristics are recovered upon exposing the device to ambient conditions. Thus, CNTFETs that will exhibit permanently p- or n-characteristics are needed. Recently, we have shown that boron-doped SWNT bundles exhibit permanently p-type characteristics, which suggests that nitrogen-doped isolated SWNTs may lead to perma- nently n-type devices [8]. In this Letter, we report a sim- ple liquid injection chemical vapor deposition (CVD) method for synthesizing nitrogen-doped isolated SWNTs. The nitrogen concentration in the nanotubes is varied by changing the concentration of acetonitrile in the feed, and micro-Raman spectroscopy is used to study the effect of doped nitrogen in the SWNTs. Raman scattering is an excellent probe for investigat- ing the electronic and phonon structure in pristine and doped SWNT materials due to the resonant coupling of the laser excitation energy to the transition energies between the van Hove singularities in the electronic den- sity of states (DOS) [9]. There are three basic groups of Raman-active bands in SWNTs that reveal distinctive structural and electronic properties. The in-phase vibra- tion of carbon atoms in the direction perpendicular to the nanotube axis, called the radial breathing mode (RBM), is usually observed between 100 and 300 cm 1 0009-2614/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2005.07.007 * Corresponding author. Fax: +1 864 656 0805. E-mail address: arao@clemson.edu (A.M. Rao). www.elsevier.com/locate/cplett Chemical Physics Letters 412 (2005) 269–273